It seems indeed related to the let’s encrypt issue.
I would suggest to try:
- if you are using docker in production, run a
curl https://api.forestadmin.comfrom the host & inside the container - if you are not using docker in production, just run a
curl https://api.forestadmin.comon your production machine
Depending on the response (404 or SSL issue), share the response here and I will help to further investigate 
If you want, we also have a lot of thread discussing about this issue with a few different solutions (That are depend on the way you are hosting your production environment).
- What to do when you get "SSL_connect returned=1 errno=0 state=error: certificate verify failed (self signed certificate in certificate chain)"
- 🚨 Forest down (SSL issue) - Trouble logging in - error 400: Invalid client id 🚨
- Let's Encrypt CA expiration
(Search for either SSL/Let’s encrypt related threads)